Microwave energy is a particularly convenient method of heating wet material to dry it as described in German patent document 3,814,451 of H. K. Werner, European patent application 333,423 of N. Arai, and Japanese patents 2-52981 and 63-299086. In addition equipment is known which simultaneously agitates or mixes particulate material while irradiating it with microwave radiation. See German patent documents 3,907,248 and 3,923,841 respectively of B. Lelanz and K. Satow, German Utility Model 8,904,885, French patent 2,641,491 of R. Patrick, and U.S. Pat. Nos. 3,777,095 and 3,834,038 respectively of T. Muranaka and R. Janda.
A standard auger-type mixer, such as described in U.S. Pat. No. 3,775,863 of L. Updegrove, has a basically conical and upwardly flared housing in which is provided an auger having an upper end mounted on the outer end of an arm whose inner end is pivoted in the cover of the housing about its central axis so that rotation of the arm orbits the auger inside the housing, churning the contents thereof. The walls and/or auger of such a device are heated to transmit heat to the contents and dry them. In an improvement on such a device to be used for drying particulate material, European patent application 306,563 of I. Sato proposes mounting a magnetron, that is a microwave emitter, in the cover of the housing.
Such an arrangement is fairly effective, but the orbiting auger arm periodically passes underneath the magnetron, blocking it and causing it to heat the auger drive rather than the actual contents of the housing.